From research carried out in various laboratories, it is known that there is a significant proliferation of bacteria and like micro-organisms during storage periods in a medium which contains nutritive elements with respect to these micro-organisms. This is the case even if the medium does not contain originally any significant level of such micro-organisms.
The problem arises particularly in the case of mineral water stored in bottles and other viscous or fluid media found in containers and stocked for long periods by stores, warehouses and the like. Analysis of mineral water stored in bottles shows that the micro-organism content is at least 10 times greater for water stored in plastic bottles than for water stored in glass bottles. This is a result of the fact that the plastic bottles contain substances, as noted below, which provide a nutritive medium for micro-organisms and promote reproduction even where the water has been sterilized so that only miniscule quantities of the micro-organism may be present originally.
The problem is significant since the use of mineral water and other liquid beverages or the like in plastic bottles is constantly increasing.
While various bacterial species are commonly found in water stored in glass bottles, other species are found to develop in bottles of synthetic-resin materials. This demonstrates that the synthetic-resin material plays the role of a nutritive medium, probably because of the presence of substances of low molecular weight, such as plasticizers and lubricants, in the synthetic-resin material as required for fabrication of plastic bottles. Such substances are able to form, on the surface of a plastic bottle, linear chains which favor the development of bacteria or germs. It is also known that the proliferation of bacteria in plastic bottles for the storage of water is a function of the composition of the water itself, notably the level of its mineral salts.
While most of the micro-organisms have little effect, there is always the danger of a toxic condition developing since the micro-organisms may attain a level of 10.sup.5 or 10.sup.6 germs per cm.sup.3. At these levels, the contaminated water is able to produce intestinal indisposition in children and adults.
Another example of a nutritive medium which may become contaiminated by micro-organisms is to be found in the cosmetic field.
As is known, cosmetic compositions are highly complex and especially so in comparison with table water. Generally such cosmetic compositions are emulsions having for the most part, a continuous aqueous phase and are not suitable subjects for sterilization techniques using thermal processes.
The protection of cosmetics by incorporating in them antiseptic substances is less than perfect. For example, the esters of parahydroxybenzoic acid cause allergic dermititis and irritation of the skin at doses which are sufficient to prevent proliferation of certan Gram-negative bacteria such as pseudomonas sp.
The latter germs are capable of metabolizing the antiseptic and diminishing its concentration, thereby promoting the development of other species of micro-organisms. The problem is complicated further by a supplemental pollution during the use of the cosmetic, i.e. from contact with the skin, which may be a source of infection.
It is well known that a sterilization process may consist of introducing ions of at least one transition metal, especially ions of silver (Ag.sup.+), into water. Such processes utilize the bactericidal action which is well-known to be associated with certain transition metals, namely, the ions of the following metals: chromium, copper, zinc, cadmium, antimony and mercury.
This bactericidal action is generally described as an oligodynamic effect of the transistion metals. It is indeed surprising that relatively small quantities of such metals, particularly silver, may be used to sterilize water and yet create a system which is nontoxic to the human environment. Since silver and others of the oligodynamic metals mentioned previously form salts with contents of the digestive tract, they may be eliminated with food waste and do not tend to accumulate in the organism or, at most, accumulate only slightly.
In the case of silver, 15 to 30 grams of this substance in the human organism creates a disorder which has been denominated argyria, characterized by a blueish coloration of the skin and well known in the 19th century when curative doses of silver werre administered to patients for the treatment of certain nervous disorders. However, the amount of silver which accumulates in human organism is substantially below this toxic quantity when silver is used as a bactericidal agent in the treatment of water.
It has been calculated that a person drinking daily a liter of water containing 0.015 mg of silver per liter accumulates in his organism 3.75 g of the metal after 70 years. This quantity is significantly lower than the toxic quantities mentioned previously.
In order to introduce silver ions into water according to known sterilization processes as mentioned above, it is the general practice to bring the water into contact with pure silver in the metallic state. This may be done by immersing a plate or a wire of silver in water. Thus, where it is desired to sterilize water to be stored in a container, one need only provide a metallic silver layer along an internal wall of the vessel or as a coating on a projecting member reaching into the liquid.
In another sterilization process, the silver ions are produced by electrolytic solubilization of a silver electrode in water. For this purpose at least two electrodes of silver are generally provided.
While the latter techniques have been employed with success in the sterilization of water, especially in the case of sterilizing water for municipal distribution at reservoirs feeding municipal distribution lines and with flowing water in fisheries and the like, they have the significant disadvantage that it is not possible to bring sufficient silver into solution to inhibit proliferation of micro-organisms in the presence of a nutritive environment. In other words, the system is operable where nutrients are not present or are present in only extremely small concentrations, but has not been found to be successful in systems which can be considered nutrient media.
Thus with respect to stored water (e.g. mineral water) in plastic vessels, fruit juices, vegetable soup and the like which have high nutrient value for micro-organisms, it is not possible to provide by the aforementioned techniques a sufficiently high level or concentration of silver to ensure continued bactericidal action.
Thus the usual approach to such nutritive systems has been the use of thermal sterilization or the like, techniques which are not suitable for completely effective sterilization for the aforementioned products.
Cosmetics, in the form of liquids or pastes, constitute a prime example of systems which cannot be readily sterilized by conventional techniques including those in which the silver concentration is raised by contact of the liquid phase with a pure silver wire. These systems contain nutritive components which give rise to a high rate of proliferation of the micro-organisms so that inhibition of such proliferation is a great problem. In fact, such cosmetics had to be manufactured heretofore in highly aseptic conditions and must be stored aseptically in their receptacles. However, once the cosmetic receptacle is opened, all hope of maintaining a sterile condition must fail. Inevitably, the repeated opening and closing results in an inoculation of the medium with microbial species present in the atmosphere, on the skin of the user, or upon the walls of the environment in which the cosmetic is stored or used.